This invention improves on pivot shoes for double-hung windows that can pivot open as well as move vertically up and down. Pivot shoes for such windows are connected to the lower rails of each sash by pivot bars and move up and down in jamb channels aligned with the sash stiles. They also connect to the lower ends of sash balances that counterbalance each sash so that it will stay at any set position. The art has developed many such pivot shoes, all intended to serve similar functions that include interlocking with the jamb channel when the sash is pivoted open. Some pivot shoes use an interference grip with the jamb channel for this, and others have used biting edges or hooks.
Problems remain, however, especially with jamb channels of extruded resin that rare slipperier and more resilient than aluminum jamb channels. Also, heavier, double-glazed sash and correspondingly stronger sash balances place a greater locking load on pivot shoes. In addition, previous pivot shoes have suffered various malfunctions or disadvantages.
My improved pivot shoe uses a cam and bite spring arranged in a way that ensures stronger locking ability and greater compatibility with jamb channels made in different configurations of different materials. It is also economical to make and more reliable in operation.